WO2016174973A1

WO2016174973A1 - Working oil for hydraulic shock absorber, and hydraulic shock absorber

Info

Publication number: WO2016174973A1
Application number: PCT/JP2016/059901
Authority: WO
Inventors: クリスティアンショルツ; 義浩伊藤; 慎治加藤
Original assignee: Ｋｙｂ株式会社
Priority date: 2015-04-28
Filing date: 2016-03-28
Publication date: 2016-11-03
Also published as: US20180305634A1; KR20170128346A; EP3290496A1; CN107532099A; EP3290496A4; JPWO2016174973A1

Abstract

[Problem] To provide a working oil for shock absorbers which is inhibited from affecting rubber materials. [Solution] A working oil which comes into contact with a rubber material, characterized by comprising a polyalkylene glycol and one or more base oils selected from among fatty acid diesters, poly(α-olefin)s, and the lubricating oils classified as GIII by American Petroleum Institute (API). With this working oil, it is possible to reduce the degree of swelling of rubber materials such as sealing materials and hence use conventional rubber materials as they are.

Description

Hydraulic oil for hydraulic shock absorber and hydraulic shock absorber

The present invention relates to hydraulic oil for hydraulic shock absorbers.
More specifically, the present invention is a technology for improving the influence of chemically synthesized oil on rubber materials that come into contact with chemically synthesized oil. More specifically, the present invention controls swelling of rubber material by hydraulic oil used in shock absorbers made of chemically synthesized oil. Therefore, the influence of the base oil on the rubber material is reduced by mixing the base oil having the property of shrinking the rubber material into the chemically synthesized oil.
In addition, the present invention improves the steering stability when the vehicle is running, particularly when used for a shock absorber of a vehicle, and the vehicle travels by receiving lateral force due to the road having minute steps. In particular, the present invention relates to a hydraulic fluid for shock absorbers that can improve the ride comfort, and a shock absorber that uses this hydraulic fluid.

In automobile-related technologies, swelling and deterioration of rubber materials due to lubricating oils are a major issue in terms of durability of members and oil leakage, and improvements have been made in various technical aspects. In particular, approaches from oil seal materials and lubricant materials have been made. For example, with respect to the technology for preventing the swelling of the oil seal material, research and development have been conducted from the viewpoint of the material of the oil seal, the additive added to the base oil, the composition of the base oil, and the like.

As oil seals for automobiles, the use of acrylic rubber (ACM), fluorine rubber (FKM), nitrile rubber, urethane rubber (U), silicone rubber, hydrogenated nitrile rubber, and blends thereof is known. An example of a proposal for improving the durability of a rubber material by controlling the influence of swelling on the seal material by oils is, for example, an oil seal for automobiles having an elastic member having a seal lip portion, and the elastic member Is obtained by co-coagulating acrylonitrile butadiene rubber (A) and fluororesin (B) to obtain a co-coagulated composition, and then crosslinking acrylonitrile butadiene rubber (A). Resin (B) is a perhalopolymer oil seal for automobiles (Patent Document 1) and can maintain cold resistance and heat resistance for a long time. Has low swelling due to the base oil of the grease, and as a highly reliable sealing device, and as a rubber composition therefor, acrylonitrile butadiene rubber A having an acrylonitrile content of 18 to 26% and acrylonitrile butadiene having an acrylonitrile content of 30% or more. Roller bearing seal comprising a rubber composition containing, as a rubber component, a mixed acrylonitrile butadiene rubber in which a weight ratio of acrylonitrile butadiene rubber A: acrylonitrile butadiene rubber B = 70: 30 to 90:10 (Patent Document) 2).

Examples of improving the swelling or oil resistance of rubbers with additives added to lubricating oils and hydraulic oils are phosphorus-containing compound metals that are easy to prepare, have no adverse effects such as swelling of rubber seals, and have excellent storage stability as a lubricating oil additive composition comprising a salt, a kinematic viscosity of 100 ° C. is ^{0.5 ~ 4.5mm 2 / s,%} C a of 3 or less, and sulfur content is 0.05 mass% or less For lubricating oil comprising a hydrocarbon solvent selected from mineral oil, hydrocarbon-based synthetic oil and mixtures thereof containing 10 to 90% by mass of a metal salt of a phosphorus-containing compound having a specific chemical structure based on the total amount of the composition An additive composition (Patent Document 3) and an additive composition for lubricating oil (Patent Document 4) containing a metal salt of a phosphorus-containing compound having a different chemical structure from the additive composition have been proposed.

Examples of combinations of additive and base oil characteristics include good low-temperature characteristics, low pipe resistance, less rate of change in damping force due to temperature change, and smaller seal material swelling rate (volume change rate) Hydraulic oil for shock absorbers, comprising a base oil and a polymethacrylate viscosity index improver having a weight average molecular weight of 200,000 to 600,000 and an amine salt of an acidic phosphate ester A composition ratio of the polymethacrylate-based viscosity index improver is 0.1 to 5.0% by mass with respect to the total amount of the composition, and a composition ratio of the amine salt of the acidic phosphate ester There was 2.0 to 5.0% by weight, based on the total amount of the composition, as the properties of the composition, 40 ° C. kinematic viscosity of 4 ~ 8mm ² / s, Brookfield viscosity at -30 ° C. 1000 mP · S or less, aniline point of 85 ~ 110 ° C., shock absorber hydraulic fluid composition a viscosity index of 150 or more (Patent Document 5) have been proposed.

Examples of the base oil composition include a lubricating oil (Patent Document 6) having improved low-temperature flow and rubber swellability comprising a lubricating oil mainly composed of one or more diesters having a specific structure, and 600 There has been proposed a lubricating oil for car air conditioners (Patent Document 7) having a low swelling ratio with respect to acrylonitrile butadiene rubber by using a polyoxypropylene glycol dialkyl ether compound having an average molecular weight of ˜2000 as a base oil.

On the other hand, various vehicles such as automobiles are provided with a shock absorber for attenuating vibrations generated during traveling. The shock absorber usually includes a cylinder, and a piston and a piston rod that supports the piston are provided in the cylinder. The cylinder is separated into two oil chambers by the piston. The piston moves according to the expansion and contraction of the shock absorber, and the oil moves between the two oil chambers. The oil moving path is provided with an orifice, a valve and the like having a relatively small channel area as a damping force generating part. Damping force is generated by fluid resistance when passing through these narrow flow paths, and friction in sliding parts such as oil seal / piston rod, piston rod / guide bush, piston band / cylinder of shock absorber is controlled. Thus, the vibration suppression effect has been improved (see, for example, Patent Document 8).

As described above, the shock absorber uses a hydraulic resistance, that is, a damping force generated when oil passes through several orifices and valves provided in the piston at high speed.
Here, when the oil viscosity is μ, the oil density is ρ, the piston speed is V, and the damping force is F, the damping force F is
F = A (αμv + βρv2)
(A is a constant specific to the shock absorber, and α and β are constants specific to the oil).
A is determined by the shock absorber type, and the damping force F is affected by the oil viscosity, density, and piston speed, and the required oil viscosity and density are determined for each shock absorber type.

It is clear that the oil density is one factor that determines the damping force, as seen from the above mathematical expression for the damping force, but there are some proposals that focus on the oil density including other purposes. ing.
For example, a low-density lubricating oil is advantageous for energy saving. A lubricating base oil having a high viscosity index and excellent low-temperature fluidity, a high viscosity index using the base oil, high shear stability, high It is a hydrocarbon-based lubricating base oil having a high flash point and low density lubricating oil composition as a lubricating oil composition, and having a viscosity index of 130 or more, and a paraffin by ring analysis. A lubricating oil composition is proposed in which the CCS viscosity at −35 ° C. is 3,000 mPa · s or less, and the density is preferably 0.84 g / cm ³ or less. (Patent Document 9).
In addition, as a lubricating oil composition for a shock absorber that has excellent riding comfort in a low-temperature environment and a high-temperature environment and can suppress deterioration in riding comfort over time due to volatilization and shearing of the lubricating oil, (A) 1 to 15 base oil having a pour point of less than −40 ° C. and a kinematic viscosity at 80 ° C. of 2.0 to 2.7 mm ² / s, and (B-1) a polymethacrylate having a weight average molecular weight of 10,000 or more and less than 100,000. (B-2) a shock absorber lubricating oil composition comprising 0.1 to 5% by mass of polymethacrylate having a weight average molecular weight of 100,000 or more and 200,000 or less, and component (A) From the viewpoint of generating appropriate damping force, it is preferable that the base oil has a density of 0.80 to 0.83 g / cm ³ at 15 ° C. (Patent Document 10).

A lubricating oil composition having excellent thermal oxidation stability, lubricity, water resistance, and filtration characteristics has a kinematic viscosity at 40 ° C. of 25 to 53 cSt, a viscosity index of 130 to 150, and a density at 15 ° C. of 0.80 to The lubricating oil composition is 0.84 g / cm ³ , has a flash point of 252 ° C. or higher, and contains a primary amine having C8 to C20 tertiary alkyl in the lubricating oil composition. Densification can reduce the delivery pressure loss and at the same time improve flow efficiency, and the delivery pressure loss in the hydraulic line is converted to heat and sound, so heat generation and noise are suppressed by reducing the density. Has also been suggested (Patent Document 11)

JP 2014-178014 A JP 2013-181985 A JP 2011-162723 A JP 2009-227769 A JP2011-21111A JP-A-9-1000048 JP-A-8-311473 JP 2000-192067 A JP 2012-180535 A JP 2015-40299 A JP 2004-250504 A

The shock absorber is a functional component that plays an important role in maneuverability, stability, and ride comfort among automotive suspension components. Various types of shock absorbers are known, but basically they are composed of a piston and a cylinder, and hydraulic fluid is sealed inside, and the piston and cylinder, piston rod and cylinder sliding surfaces are internally The hydraulic fluid is sealed with a sealing material such as nitrile rubber so as not to leak out and to protect the sliding portion. The impact applied from the outside of the automobile is absorbed by the damping force using the flow resistance of the hydraulic fluid enclosed inside. The hydraulic fluid for shock absorbers having such functions is required to have various performances such as damping force characteristics, low-temperature fluidity, wear resistance, low friction characteristics, seal compatibility, and prevention of oil leakage. In order to satisfy the requirements, various hydraulic oils for shock absorbers, hydraulic oil additives and seal materials have been proposed.

Conventionally, in shock absorbers, rubber materials that match the characteristics of mineral oil base oil, which is a lubricating oil, have been used as sealing materials, but the inventors have combined these rubber materials with chemically synthesized oils. The problem that it is difficult to use chemically synthesized oil because the sealing material may cause quality deterioration is found, and it is difficult to use chemically synthesized oil by reducing the quality deterioration due to the swelling property of current rubber materials. It was an object of the present invention to make it possible to use existing rubber materials without any change.

Conventionally, shock absorbers are used to absorb vibrations caused by road surface irregularities and improve the riding comfort and maneuverability of automobiles, and the damping force by shock absorbers is affected by oil viscosity, density, piston speed, etc. It is known, but details about how the oil density affects the ride quality and maneuverability of the car were unknown. Conventionally, hydraulic oil having a density of about 0.83 to 0.86 g / cm ³ has been usually used for shock absorbers. The present invention focuses on the density of hydraulic oil used in hydraulic shock absorbers of automobiles in the current state of the art, and improves the ride comfort and maneuverability by performing tests with actual vehicles. The purpose was to develop new technical means.

The inventors of the present invention have developed a hydraulic oil that comes into contact with a rubber material by accumulating intensive studies so that the current rubber material can be used without change, and includes polyalkylene glycol, fatty acid diester, polyalpha A hydraulic oil characterized in that it contains one or more base oils selected from olefins and lubricating oils similar to GIII in the American Petroleum Institute (API) has been reached.
That is, the present invention makes it possible to use a chemically synthesized oil as a lubricating oil by a minimum material change of adjusting the composition of the base oil, and can reduce the swelling property of the rubber material by the chemically synthesized oil. The effect of chemically synthesized oil on the rubber material is reduced by mixing lubricating oil having characteristics. The present invention is particularly suitable as a hydraulic oil for high-density shock absorbers, and is particularly useful as a lubricating oil based on fatty acid diesters and / or polyalkylene glycols, and also has improved steering stability and ride comfort. An improved shock absorber can be provided.

In addition, the present inventors have focused on the influence of the characteristics of hydraulic oil used in hydraulic shock absorbers in order to improve the maneuverability and ride comfort of passenger cars, among other automobiles, and have accumulated research and development. , A hydraulic shock absorber hydraulic oil based on a fatty acid diester and / or a polyalkylene glycol, wherein the hydraulic oil has a density of 0.87 g / cm ³ or more at a temperature of 15 ° C. It has reached the hydraulic fluid for absorber. The present invention is a hydraulic shock absorber hydraulic oil based on a fatty acid diester and / or polyalkylene glycol, and the density of the hydraulic oil is 0.87 g / cm ³ or more at a temperature of 15 ° C. It improves the ride comfort and handling stability of automobiles and motorcycles, particularly passenger cars.

That is, the present invention is a hydraulic oil based on a fatty acid diester and / or a polyalkylene glycol, wherein the hydraulic oil has a density of 0.87 g / cm ³ or more at a temperature of 15 ° C. The gist is oil.

The ratio of the PAG in hydraulic fluid, the volume change of the rubber material in hydraulic fluid, and the change of the density of hydraulic fluid are shown. The comprehensive evaluation range of the operating stability and ride comfort of the tested hydraulic oil is shown for each friction and density. The sensory test result in the actual vehicle test of the hydraulic oil which adjusted the density of Example 1-4 is shown. The sensory test result in the actual vehicle test of the hydraulic oil which adjusted the friction of Example 1-4 is shown. The result of having put together the sensory test which changes with friction and the density of Example 1-4 is shown. The sensory test result in the actual vehicle test of the hydraulic oil which adjusted the density of Example 2-2 is shown. The sensory test result in the actual vehicle test of the hydraulic oil which adjusted the friction of Example 2-2 is shown. The result of having put together the sensory test which changes with friction and density of Example 2-2 is shown.

The present invention is a shock absorber hydraulic oil that comes into contact with a rubber material, and is selected from polyalkylene glycols, fatty acid diesters or polyalphaolefins, and lubricating oils classified as GIII by the American Petroleum Institute (API) classification. The present invention relates to a shock absorber hydraulic oil that controls the swelling property of a rubber material, characterized in that it contains more than one type of base oil. It has been found that the use of a chemically synthesized oil based on polyalkylene glycol as a hydraulic oil for shock absorbers reduces the oil resistance by swelling the rubber material constituting the oil seal or the like.
The present invention is based on the finding that swelling or deterioration of a rubber material due to hydraulic oil is prevented by containing a fatty acid diester having a property of shrinking the rubber material.
In addition, the present invention appropriately sets a mixing ratio of a polyalkylene glycol and a fatty acid diester, a polyalphaolefin, and one selected from lubricating oil classified as GIII in the classification of the American Petroleum Institute (API). It can be put to practical use as a high-density hydraulic oil, and is suitable for use as a shock absorber with improved driving stability and ride comfort. And it makes it possible to use chemically synthesized oil without changing the rubber composition of the rubber member used conventionally.

Furthermore, the present invention is a hydraulic shock absorber hydraulic oil based on a fatty acid diester and / or a polyalkylene glycol, and the density of the hydraulic oil is 0.87 g / cm ³ or more at a temperature of 15 ° C. It is related to hydraulic fluid for shock absorbers, which can achieve both high ride comfort and handling stability at a high level. Conventionally, a low-density mineral oil can be used as the base oil. It is possible to improve the performance of the vehicle by changing the place where there were many to high-density chemically synthesized oil.

Conventionally, it has been known that the hydraulic oil density is related to the damping force of the shock absorber, but the present inventors have reached the present invention by examining in detail the mechanism that the hydraulic oil density affects the damping force. did. As a result, damping force is related to frictional force and oil pressure. The sliding member and the hydraulic oil affect the frictional force, and the valve and the hydraulic oil affect the oil pressure. Therefore, we examined how the characteristics of hydraulic oil related to both frictional force and hydraulic pressure affect the damping force.
First, attention was paid to the density of the hydraulic oil among various characteristic values relating to the frictional force and hydraulic pressure required for the hydraulic oil, and good results were obtained by setting it higher than the conventional value. Further, the damping force could be further improved by setting the friction coefficient of the hydraulic oil low.

The improvement of the oil resistance of the rubber member according to the present invention will be specifically described with reference to FIG. FIG. 1 shows the ratio of PAG in the base oil composed of polyalkylene glycol (PAG) and fatty acid diester, the volume change of the rubber material, and the density of the hydraulic oil. The horizontal axis represents the proportion of PAG in the base oil, and the remaining proportion is fatty acid diester. The vertical axis represents the volume change of the rubber material and the density of the base oil. This test is a result of measuring the volume change of acrylonitrile butadiene rubber immersed in hydraulic oil of each composition in the figure at a temperature of 100 ° C. for 72 hours, and shows the swelling property of the rubber material.
For example, an oil seal used for a shock absorber or the like is required to suppress a volume change rate in hydraulic oil to + 15% or less. FIG. 1 clearly shows that the volume change rate is reduced by using PAG as a base oil and adding a fatty acid diester. In this example, by adjusting the PAG to be about 95% by weight or less, the volume change rate becomes a preferable range, and at the same time, the density can be maintained at a high density of 0.95 g / cm ^3. It is shown that.

The present invention relates to a polyalkylene glycol and one or more ratios selected from fatty acid diesters, polyalphaolefins, and lubricating oils classified as GIII in the American Petroleum Institute (API) (hereinafter, both are also simply referred to as lubricating oils). If the volume change rate of the rubber material can be controlled to + 15% or less, there is no problem, but the lubricating oil added and mixed to maintain a density of 0.92 g / cm ³ or more is 60 to 5% by weight. The range is preferably 40 to 5% by weight in order to maintain the density of 0.89 g / cm ³ or more.
The hydraulic oil blended within these numerical ranges can control the swelling of the rubber material and can be a high-density hydraulic oil. A vehicle adopting a high-density shock absorber hydraulic oil of 0.89 g / cm ³ or more has improved driving stability and ride comfort.

Next, the fatty acid diester and polyalkylene glycol, which are the base oil of the hydraulic oil of the present invention, will be described.
As the fatty acid diester and the polyalkylene glycol, those having the structure described below are used.

[Polyalkylene glycol (PAG)]
As polyalkylene glycol, it consists of 1 type, or 2 or more types chosen from the group which consists of a compound denoted by the following general formula, for example.
R ₁ —O— (R ₂ —O) _n —R ₃ (IV)
[In Formula (IV), R ₁ and R ₃ may be the same or different, each represents a hydrogen atom or an alkyl group, R ₂ represents an alkylene group, and n represents a compound represented by Formula (IV). An integer having a weight average molecular weight of 300 to 2000 is preferred. ]

When one or both of R _{1 and} R _{3 in} formula (IV) is an alkyl group, the carbon number of the alkyl group can be arbitrarily selected, but the carbon number of the alkyl group is 1 to 18 Preferably, it is 1-10. The alkyl group may be linear or branched. Specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, linear or branched pentyl group, linear chain Linear or branched hexyl group, linear or branched heptyl group, linear or branched octyl group, linear or branched nonyl group, linear or branched Decyl group, linear or branched undecyl group, linear or branched dodecyl group, linear or branched tridecyl group, linear or branched tetradecyl group, linear And a linear or branched pentadecyl group, a linear or branched hexadecyl group, a linear or branched heptadecyl group, and a linear or branched octadecyl group.

Further, the number of carbon atoms of the alkylene group represented by R ₂ in the formula (IV) is not particularly limited, but in general, it is preferably 2 to 10 carbon atoms. Specific examples of the alkylene group having 2 to 10 carbon atoms include ethylene group, propylene group (including 1-methylethylene group and 2-methylethylene group), trimethylene group, butylene group (1-ethylethylene group and 2 -Ethylethylene group), 1,2-dimethylethylene group, 2,2-dimethylethylene group, 1-methyltrimethylene group, 2-methyltrimethylene group, 3-methyltrimethylene group, tetramethylene group, pentylene Groups (including 1-butylethylene group and 2-butylethylene group), 1-ethyl-1-methylethylene group, 1-ethyl-2-methylethylene group, 1,1,2-trimethylethylene group, 1,2 , 2-trimethylethylene group, hexylene group (including 1-butylethylene group and 2-butylethylene group), 1-methyl-1-propylene Ethylene group, 1-methyl-2-propylethylene group, 2-methyl-2-propylethylene group, 1,1-diethylethylene group, 1,2-diethylethylene group, 2,2-diethylethylene group, 1-ethyl -1,2-dimethylethylene group, 1-ethyl-2,2-dimethylethylene group, 2-ethyl-1,1-dimethylethylene group, 2-ethyl-1,2-dimethylethylene group, 1,1,2 , 2-tetramethylethylene group, heptylene group (including 1-pentylethylene group and 2-pentylethylene group), octylene group (including 1-hexylethylene group and 2-hexylethylene group), nonylene group (1-heptyl group) Ethylene group and 2-heptylethylene group), decylene group (including 1-octylethylene group and 2-octylethylene group), etc. It can gel.

The compound represented by the formula (IV) may be a homopolymer having one R _{2 in} the same molecule or a copolymer having two or more R ₂ in the same molecule. . Furthermore, when the compound represented by the general formula (1) is a copolymer, the monomer ratio and the monomer arrangement constituting the copolymer are not particularly limited, and a random copolymer or an alternating copolymer is included. And a block copolymer.
When the compound represented by the formula (IV) is a homopolymer, R ₂ is preferably an alkylene group having 4 to 6 carbon atoms, and more preferably a butylene group from the viewpoint of availability of raw material monomers. preferable. In the case where the compound represented by the general formula (IV) is a copolymer, R ₂ is preferably an alkylene group having 3 to 6 carbon atoms. Or it is more preferable that it is a butylene group.
N in the formula (IV) is an integer such that the compound represented by the general formula (IV) has a weight average molecular weight of 300 to 2000, preferably 500 to 1800, more preferably 800 to 1500.

Specific examples of the polyalkylene glycol include, for example, ethylene oxide, propylene oxide, butylene oxide, or a mixture thereof, preferably propylene oxide, as alkylene oxide. Preferred examples include polyethylene glycol having a molecular weight of 1000 to 5000, polypropylene glycol, polypropylene glycol monobutyl ether, polypropylene glycol butyl methyl diether, and a decanol compound having a molecular weight of 1030 or 770 having a propoxy group butoxy group. Both ends of the molecular chain are alkyl groups, one end is an alkyl group, the other end is a hydroxyl group, and both ends are hydroxyl groups. The terminal alkyl group has 1 to 18 carbon atoms.

[Fatty acid diester]
As fatty acid diester used by this invention, the compound which has the following molecular formula can be mentioned, for example.
[Dibasic fatty acid and alcohol ester]
R ₁ —O—CO—A—CO—R ₂ (I)
R ₁ — (O) — (CH ₂ ) _n —O—CO—A—CO—O— (CH ₂ ) _n — (O) —R ₂ (II)
(A is an alkylene group having 1 to 20 carbon atoms, n is an integer of 0 to 2, R ₁ and R ₂ are alkyl groups, aromatic alkyl groups, aromatic groups and alicyclic alkyls which may have a substituent. Group.)
A specific example of the fatty acid diester used in the present invention is a fatty acid diester in which a carboxylic acid ester is bonded to an alkylene group having 1 to 10 carbon atoms or an alkylene group which may contain oxygen in the main chain. be able to. Specifically, the dibasic acid is an acid having 1 to 18 carbon atoms, such as adipic acid, azelaic acid, sebacic acid, phthalic acid, succinic acid, glutaric acid, piperic acid, suberic acid, azelaic acid, undecane. Examples include diacid, dodecanedioic acid, brassic acid, tetradecanedioic acid and derivatives thereof.
Moreover, the following alcohols can be mentioned as an example of alcohol.
Examples of the aliphatic alcohol include methyl alcohol, ethyl alcohol, propyl alcohol, and capryl alcohol; examples of the aromatic alcohol include phenol, cresol, xylenol, alkylphenol, benzyl alcohol, phenethyl alcohol, and phenoxyethanol; and examples of the alicyclic alcohol include cyclo Hexanol, methylcyclohexanol, cyclohexanemethanol, norbornanemethanol, borneol, isoborneol, etc .; diols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, neopentyl glycol, 1,4- Butanediol, 1,6-hexanediol, etc .; Glycerin, and trimethylol propane.

[Esters of polyols and bimolecular dibasic fatty acids]
R ₁ —CO—O—A—O—CO—R ₂ (III)
For example, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, neopentyl glycol, 1,4-butanediol, 1,6-hexanediol and C3-C18 linear or branched fatty acids Can be mentioned.

Specific examples of the fatty acid diester include, for example, dibenzyl isophthalate, phenylacetic acid diester of diethylene glycol, phenylacetic acid diester of butanediol, phenylacetic acid and benzoic acid ester of 1,4-butanediol, 1,4-butanediol Benzoic acid diesters of triethylene glycol, benzoic acid diester of triethylene glycol, benzoic acid diester of traethylene glycol, di (1-ethylpropyl) adipate, di (1-ethylpropyl) azelate, di (isobutyl) sebacate, etc. .

In the present invention, examples of the polyalphaolefin added to and mixed with the base oil and the base oil for lubricating oil classified as GIII by AIP are as follows.
[Polyalphaolefin (PAO)]
The polyalphaolefin contained in the hydraulic oil of the present invention is exemplified below.
Polyalphaolefins (poly-α-olefins), alpha-olefin oligomers (α-olefin oligomers), or mixtures thereof (polyalphaolefins and alphaolefin oligomers). The polyalphaolefin is a polymer of various alphaolefins (monomers). The polyalphaolefin may be a mixture in which a plurality of “polymers of alpha olefins (monomers)” are mixed. The alpha olefin oligomers are oligomers of various alpha olefins (monomers), and also include hydrogenated alpha olefin (monomer) oligomers. The alpha olefin oligomer may be a mixture of a plurality of types of “alpha olefin (monomer) oligomers” or a mixture of a plurality of types of “hydrogenated alpha olefin (monomer) oligomers”. It may be. Further, the alpha olefin oligomer may be a mixture of “alpha olefin (monomer) oligomer” and “hydrogenated alpha olefin (monomer) oligomer”.

The alpha olefin (monomer) is not particularly limited, and examples thereof include ethylene, propylene, butene, and alpha olefins having 5 or more carbon atoms. In the production of a polyalphaolefin or an alphaolefin oligomer, one of the above alpha olefins (monomers) may be used alone, or two or more may be used in combination. The polyalphaolefin may be produced by homopolymerizing one kind of alphaolefin, or may be produced by copolymerizing two or more kinds of alphaolefin. That is, the polyalphaolefin may be a homopolymer of one kind of alpha olefin (monomer) or a copolymer (copolymer) of two or more kinds of alpha olefins.

[Base oils for lubricants classified as GIII by AIP]
The lubricating oil base oil classified as GIII in the AIP contained in the hydraulic oil of the present invention is specified by the API as having a sulfur content of 0.03% or less, a saturation content of 90% or more, and a viscosity index of 120 or more. Because it is manufactured by a process based on hydroprocessing, it has a low sulfur content, a high saturation content, and is obtained by decomposing and modifying crude oil-derived raw materials into a molecular structure suitable for lubricating oil. It has the characteristics of little change (high viscosity index).

Examples of the rubber material whose swelling property is controlled in the hydraulic fluid for shock absorbers in which the swelling of the rubber material of the present invention is controlled include the following.
[Rubber material]
The hydraulic oil of the present invention is not particularly limited as a rubber material because it does not swell to rubber materials conventionally used for oil seals and the like. For example, nitrile rubber, hydrogenated nitrile, etc. Examples thereof include rubber and fluororubber. However, the fact that the hydraulic oil of the present invention is not swellable with respect to the acrylonitrile butadiene rubber conventionally used in oil seals means that the hydraulic oil contains fatty acid diesters or polyalkylene glycols without changing the material of the oil seal. It is a great advantage that can be used. Next, the composition of a typical nitrile rubber according to the present invention will be described.

[Nitrile rubber (NBR)]
Nitrile rubber (NBR) is a copolymer of butadiene and acrylonitrile, and is most widely used among oil-resistant synthetic rubbers. NBR has many varieties, and its individuality is determined by the acrylonitrile content (bound AN amount). When the amount of bonded AN is large, the oil resistance is improved, and when it is small (when the amount of butadiene is large), the cold resistance is increased.
HNBR (hydrogenated nitrile rubber, hydrogenated nitrile rubber) can be obtained by chemically hydrogenating residual double bonds contained in butadiene in the polymer main chain of nitrile rubber (NBR). It is easy to introduce a third monomer other than butadiene and acrylonitrile, and various modifications have been developed. There are carboxylated NBR (XNBR) in which methacrylic acid is introduced, NBIR in which part of butadiene is replaced with isoprene, NIR in which all of butadiene is replaced with isoprene, and the like. In order to improve the ozone resistance of nitrile rubber (NBR), some are blended with highly compatible PVC (vinyl chloride), and various products can be obtained depending on the blend ratio.

The present invention relates to a hydraulic shock absorber hydraulic oil comprising a polyalkylene glycol and a base oil composed of a fatty acid diester or polyalphaolefin or a lubricating oil classified as GIII in the American Petroleum Institute (API), but at a temperature of 15 ° C. The density is preferably 0.87 g / cm ³ or more. By increasing the hydraulic oil density, it is possible to achieve both a high level of driving comfort and driving stability. Conventionally, hydraulic oil, which was often based on low-density mineral oil, has a higher operating oil. It is possible to improve the performance of the vehicle at the same time by changing to a synthetic synthetic oil of density. As described below, the effect of high-density hydraulic oil has been proved by tests with actual vehicles.

Conventionally, it has been known that the hydraulic oil density is related to the damping force of the shock absorber, but the present inventors have reached the present invention by examining in detail the mechanism that the hydraulic oil density affects the damping force. did. Damping force is related to friction force and oil pressure. The sliding member and the hydraulic oil affect the frictional force, and the valve and the hydraulic oil affect the oil pressure. Therefore, paying attention to the density of the hydraulic oil among various characteristic values related to the frictional force and hydraulic pressure required for the hydraulic oil related to both frictional force and hydraulic pressure, set it higher than the conventional value. The result was good. Further, the damping force could be further improved by setting the friction coefficient of the hydraulic oil low.
Details of the density and frictional force of the hydraulic oil will be described.

[Contrast of friction and density between hydraulic oil of the present invention and conventional example]
In the present invention, three samples with substantially the same coefficient of friction and different densities and five samples with different densities and different coefficients of friction were prepared for testing with an actual vehicle. Specifically, low density medium friction oil (2), low density high friction oil (3), medium density low friction oil (4), high density low friction oil (5), low density low friction oil (6) is there. The friction coefficient was measured by a Bowden-Leven type reciprocating friction test. A test piece made of nitrile butadiene rubber and a test plate with chrome plating on the surface were set at a predetermined position of a Bowden-Leben tester, and hydraulic oil was poured between the test ball and the test plate. And it tested on the conditions of load 20N and sliding speed 0.06mm / s, and measured the friction coefficient.
The density of commercially available hydraulic oil is 0.85 to 0.86 g / cm ^{3 and the} friction coefficient is about 0.012 to 0.056. The density of the above-mentioned low density medium friction oil (2) is 0.84 g / cm ³ , the friction coefficient is 0.018, the density of the low density high friction oil (3) is 0.84 g / cm ³ , and the friction coefficient is 0. 034, the density of the medium density low friction oil (4) is 0.89 g / cm ³ , the friction coefficient is 0.008, the density of the high density low friction oil (5) is 0.939 g / cm ³ , and the friction coefficient is 0. 009, the density of the low-density low-friction oil (6) is 0.839 g / cm ^{3 and the} friction coefficient is 0.010.

Fig. 2 shows the steering stability and ride comfort by combining the evaluation results of the above-mentioned items of the sensory test with an actual vehicle. The vertical axis represents steering stability, and the horizontal axis represents ride comfort. The distance from the origin indicates better performance. In other words, it is shown that the better results are achieved as the position is higher or rightward in FIG. The diagonal lines in FIG. 2 indicate that steering stability and riding comfort are in a balanced state. In FIG. 2, a region that can be adjusted by the low-density hydraulic oil and a region that can be adjusted by the high-density hydraulic fluid are indicated by solid lines. The fact that the adjustment area by the high-density hydraulic oil is located above the adjustment area by the high-density hydraulic oil indicates that excellent results have been obtained by increasing the density of the hydraulic oil. Moreover, the area | region which can be adjusted with a low friction hydraulic fluid, and the area | region which can be adjusted with a high friction hydraulic fluid are shown with the broken line. The fact that the adjustment region with the low-friction hydraulic oil is located above the adjustment region with the medium-high friction hydraulic oil indicates that excellent results have been obtained by reducing the friction of the hydraulic oil. However, simply applying high-density hydraulic fluid will increase the damping force too much, so the evaluation result after adjusting the damping force value to a predetermined value by valve adjustment is shown as (5) 'in FIG. Show. A more balanced evaluation result can be obtained by adjusting the valve.

[Base oil density]
The density of the base oil used for the shock absorber in the present invention is preferably 0.87 g / cm ³ or more at a temperature of 15 ° C. If this value is not exceeded, the degree of improvement in handling stability and ride comfort will be small compared to conventional products. Further, the density of the hydraulic oil is preferably in the range of 0.87 to 1.0 g / cm ³ , more preferably in the range of 0.89 to 0.94 g / cm ³ .
Changes in the composition and density of the hydraulic oil are shown in FIG. It is the relationship between the ratio and density of polyalkylene glycol in the base oil containing polyalkylene glycol (PAG) and fatty acid diester, and the density of PAG is 0.96 g / cm ³ , and the density is 0.87 g / cm ³ or more. In order to obtain hydraulic oil, it is necessary to contain about 17% by weight of PAG. Further, it is possible to mix a base oil used as a working oil such as mineral oil. In order to obtain hydraulic oil having a density of 0.89 g / cm ³ or more, it is necessary to contain about 40% by weight of PAG (about 60% by weight of fatty acid diester).

[Composition of base oil]
The base oil used in the present invention contains, for example, a fatty acid diester and a polyalkylene glycol, and the density thereof is 0.87 g / cm ³ or more at a temperature of 15 ° C.
The polyalkylene glycol constituting the base oil in the present invention is not particularly limited in terms of its composition and blending ratio, but it does not matter if the density of the produced hydraulic oil is 0.87 g / cm ³ or more. Further, it is possible to mix a base oil used as a working oil such as mineral oil. It is possible to control the swelling of the rubber material of the sealing material by mixing the lubricating oil classified as GIII in the classification of polyalphaolefin or API instead of the fatty acid diester.

[Additive]
The hydraulic fluid for shock absorbers of the present invention includes additives such as viscosity index improvers, dispersants, antioxidants, friction modifiers, extreme pressure agents, metal deactivators, pour point depressants, and antifoaming agents. Can be blended.
Examples of the viscosity index improver include olefin copolymers such as polymethacrylate and ethylene-propylene copolymer, styrene copolymers such as dispersed olefin copolymers, and styrene-diene hydrogenated copolymers. , Alone or in combination of two or more.
Examples of the antioxidant include phenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4′-methylenebis- (2,6-di-t-butylphenol), alkyls Amine-based antioxidants such as diphenylamine, phenyl-α-naphthylamine, alkylated-α-naphthylamine, dialkylthiodipropionate, dialkyldithiocarbamate derivatives (excluding metal salts), bis (3,5-di-t- (Butyl-4-hydroxybenzyl) sulfide, mercaptobenzothiazole, reaction product of phosphorus pentasulfide and olefin, and sulfur-based antioxidants such as dicetyl sulfide are used alone or in combination of two or more. In particular, phenolic or amine-based compounds, zinc alkyldithiophosphates, and mixtures thereof are preferably used.

As the cleaning dispersant, for example, alkenyl succinimide is used. These detergent dispersants are usually blended in an amount of 0.1 to 10% by mass. As the metal deactivator, for example, benzotriazole, thiadiazole and the like are used alone or in combination of two or more.
As the pour point depressant, for example, polymethacrylate is used. As the antiwear agent, for example, zinc alkyldithiophosphate is used. As the antifoaming agent, for example, a silicone compound, an ester compound, or the like is used alone or in combination of two or more. As the extreme pressure agent, for example, tricresyl phosphate is used. These extreme pressure agents are usually blended in an amount of 0.1 to 10% by mass. Examples of friction modifiers include long-chain alkyl carboxylic acids and derivatives thereof, long-chain alkyl phosphates and derivatives thereof, phosphoric acid monoesters, phosphoric diesters and phosphorous acid monoesters having a hydrocarbon group having 1 to 20 carbon atoms. At least one phosphorus-containing compound selected from the group consisting of long-chain alkylamines, amides, imides and derivatives thereof, and oil-soluble molybdenum compounds are used.

[Swelling of rubber material by shock absorber hydraulic oil]
The test of the swelling property of the rubber material by the shock absorber hydraulic oil was based on the method specified in JISK6250. The swelling of the rubber material used for the shock absorber is required to be within + 15% in volume change rate.
[Measuring method of hydraulic oil density]
The measuring method of the density of the hydraulic oil is as follows, and was based on the method defined in JISK2249.
[Friction coefficient measurement method]
The coefficient of friction was measured by the following method, and was based on the method specified in the above-mentioned Bowden-Leben type reciprocating friction test.

[Test method using actual vehicle]
In examining the performance of the shock absorber hydraulic oil of the present invention with a real vehicle, using a passenger car equipped with a 3L turbo engine, the hydraulic oil of all the mounted shock absorbers is used for each test hydraulic oil. Replaced with. The evaluation at the time of running is summarized as a sensory test result by a plurality of test drivers based on a sense of each driver traveling a long distance.
The evaluation at the time of driving was summarized by the sensory test results while each driver traveled a long distance of tens of kilometers by multiple test drivers.
The test items performed evaluated high-frequency vibration in terms of ride comfort. Regarding steering stability, straight running stability, steering feeling, and roll feeling were evaluated.
The significance adopted for each evaluation item is as follows.
High-frequency vibration: High frequency input Straight-line stability: Stability when the vehicle goes straight Steering feeling: Response during steering Roll feeling: Roll speed and roll amount during steering

Density 0.939 g / cm ³ for testing, and to prepare a hydraulic oil formulation a density 0.839 g / cm ³ as the reference oil was used. These hydraulic fluids have a coefficient of friction (@ 0.06 mm / s) of about 0.01 to eliminate test results based on the difference in the friction coefficient and to control and ride only by the difference in hydraulic oil density. I grasped the influence on the comfort.
In order to eliminate the influence of the phenomenon that the damping force changes in accordance with the change in the density of the hydraulic oil, the shock absorber valve was adjusted and tested under the same conditions.
In addition, as comparative oils, two types of oils having a friction coefficient of 0.018, a medium friction oil, and a high friction oil having a friction coefficient of 0.33 were prepared with a density of 0.839 g / cm ³ and tested.

Example 1-1
In this example, the swellability of polyacrylonitrile butadiene rubber with hydraulic oil having the following composition was tested.
[Working oil composition]
Polyalkylene glycol: (polybutoxy, polypropoxy) decanol ether (MW1030) base oil 98.371 wt% x 80% = 78.697 wt%
As fatty acid diester, maleic acid isopropyl diester base oil 98.371 wt% × 20% = 19.674 wt%
A base oil composed of 98.371 wt% of the following composition was added as an additive to obtain a hydraulic oil.
0.5 wt% of a dispersant comprising a reaction product of isostearic acid and tetraethylenepentamine:
0.3 wt% of an antioxidant comprising dibutylhydroxytoluene:
0.5 wt% of friction modifier made of phosphate ester:
0.3 wt% of extreme pressure agent composed of tricresyl phosphate:
0.03 wt% of a metal deactivator comprising benzotriazole:
0.001 wt% defoamer made of dimethylpolysiloxane
The density of the hydraulic oil was 0.939 g / cm ³ according to the measurement method according to JIS 2249. The coefficient of friction was 0.009 (@ 0.06 mm / s) according to the measurement method of the Bowden-Leven type friction test.
[Test results]
The volume change rate of the rubber material by the test of the swelling property of the rubber material by the shock absorber hydraulic oil was 12.3%, which was + 15% of the specified value. In addition, it was found that the driving stability and the ride comfort were improved in the same manner as in the following examples by an actual vehicle test.

Example 1-2
In place of the fatty acid diester of Example 1, a hydraulic oil blended so that the polyalphaolefin having a pour point of −57 ° C. and a density of 0.79 was 60% by weight was prepared, and the volume change of the rubber material was measured. The change rate was within + 15%. The actual vehicle test revealed that the handling stability and ride comfort were improved as in the following examples.

(Example 1-3)
In place of the fatty acid diester of Example 1, a hydraulic oil blended so that GIII: S-oil U, S2 was 70% by weight was prepared, and when the volume change of the rubber material was measured, the volume change rate was within + 15%. Was obtained. The actual vehicle test revealed that the handling stability and ride comfort were improved as in the following examples.

(Example 1-4)
In this example, hydraulic oil having a changed coefficient of friction was produced, and an actual vehicle test of steering stability and riding comfort was performed. The used hydraulic oil is a medium friction oil (friction coefficient 0.018, density 0.84 g / cm ³ ), high friction coefficient (friction coefficient 0.33, density 0.84 g / cm ³ ), low density and friction coefficient. It is two kinds that changed. Further, a reference oil (low friction: coefficient of friction 0.01, low density: density 0.84 g / cm ³ ) was added and three types of hydraulic oil were tested under the same conditions, and the results are shown in FIG. It can be seen from FIG. 4 that by increasing the coefficient of friction, the overall steering stability is improved, but the performance related to high-frequency vibration, that is, the riding comfort is lowered.
Also, two types of hydraulic oils, high density low friction oil (density 0.939 g / cm ³ , friction coefficient 0.009) and low density low friction oil (density 0.839 g / cm ³ , friction coefficient 0.010), are used. The test was performed under the same conditions, and the result is shown in FIG. It can be seen from FIG. 3 that the steering stability salt bread is improved by increasing the density.
If the test results shown in FIG. 4 and FIG. 3 are compared and evaluated according to the running of the actual vehicle, they can be summarized as shown in FIG. Low-friction oil provides good ride comfort but poor handling stability. That is, the low friction oil cannot satisfy the ride comfort and the handling stability at the same time. In addition, high friction oil has good driving stability but not good ride comfort. That is, the high friction oil cannot satisfy the ride comfort and the handling stability at the same time. From these test results, it is recognized that the low friction oil and the high friction oil each have a defect, and that this defect cannot be overcome by adjusting the friction coefficient.
However, it has been found by combining the test results of Example 1 that these disadvantages can be overcome by hydraulic oil having both low friction and high density.

(Summary of Examples 1-1 to 4)
As described above, the inventions that can be grasped from Examples 1-1 to 4 are hydraulic oils that come into contact with rubber materials, which are polyalkylene glycols, fatty acid diesters, polyalphaolefins, and GIII in the American Petroleum Institute (API). A hydraulic oil characterized in that it contains one or more base oils selected from lubricating oils, and uses synthetic oils as lubricating oils with minimal material changes to adjust the composition of the base oil It has the effect of making it possible.

Example 2-1
[Working fluid composition of the present invention]
A base oil consisting of polypropylene glycol diester was 98.371 wt%, and the following compound was added as an additive to obtain a hydraulic oil.
0.5 wt% of a dispersant comprising a reaction product of isostearic acid and tetraethylenepentamine:
0.3 wt% of an antioxidant comprising dibutylhydroxytoluene:
0.5 wt% of friction modifier made of phosphate ester:
0.3 wt% of extreme pressure agent composed of tricresyl phosphate:
0.03 wt% of a metal deactivator comprising benzotriazole:
0.001 wt% defoamer made of dimethylpolysiloxane
The density of the hydraulic oil was 0.939 g / cm ³ according to the measurement method according to JIS 2249. The coefficient of friction was 0.009 (@ 0.06 mm / s) according to the measurement method of the Bowden-Leven type friction test.

[Reference oil]
As a reference oil to be compared, 0.839 g / cm ³ and a friction coefficient (@ 0.06 mm / s) 0.010 were prepared. Test results were evaluated relative to the reference oil. 6 and 7, a value of 0 indicates evaluation of the reference oil, and a positive value indicates that an excellent result is obtained, and a negative value indicates that an inferior result is obtained.

[Test results]
FIG. 6 shows the evaluation results of the high-density hydraulic oil and the reference oil of the present invention. High-density hydraulic oil was evaluated as having excellent high-frequency vibration, steering feeling, and straight running stability. From this test result, it has been clarified that the characteristics of both driving stability and riding comfort are improved by increasing the density of hydraulic oil.

(Example 2-2)
In this example, hydraulic oil having a changed coefficient of friction was produced, and an actual vehicle test of steering stability and riding comfort was performed. The used hydraulic oil is a medium friction oil (friction coefficient 0.018, density 0.84 g / cm ³ ), high friction coefficient (friction coefficient 0.33, density 0.84 g / cm ³ ), low density and friction coefficient. It is two kinds that changed. Further, a reference oil (low friction: coefficient of friction 0.01, low density: density 0.84 g / cm ³ ) was added, and three types of hydraulic oil were tested under the same density conditions. The results are shown in FIG. It can be seen from FIG. 7 that by increasing the friction coefficient, the overall handling stability is improved, but the performance related to high-frequency vibration, that is, the riding comfort is lowered.
If this result is evaluated according to the running of the actual vehicle by comparing the test result of the high-density oil shown in FIG. 6, it can be summarized as shown in FIG. 8, which is the same as FIG. Low-friction oil provides good ride comfort but poor handling stability. That is, the low friction oil cannot satisfy the ride comfort and the handling stability at the same time. In addition, high friction oil has good driving stability but not good ride comfort. That is, the high friction oil cannot satisfy the ride comfort and the handling stability at the same time. From these test results, it is recognized that the low friction oil and the high friction oil each have a defect, and that this defect cannot be overcome by adjusting the friction coefficient.
However, it has been found by combining the test results of Example 2-1 that these drawbacks can be overcome by hydraulic oil having both low friction and high density.

(Summary of Examples 2-1 and 2)
As described above, the invention that can be grasped from Examples 2-1 and 2 is a hydraulic shock absorber hydraulic oil based on a fatty acid diester and / or a polyalkylene glycol, and the density of the hydraulic oil has a temperature of 15 ° C. The hydraulic fluid for shock absorbers is characterized in that it is 0.87 g / cm ³ or more at the same time. By using a high-density hydraulic fluid for the shock absorber, the compressibility of the hydraulic fluid is reduced and the response of the damping force is improved. This improves the riding comfort and the handling stability.

[Summary of the present invention]
In summary, the present invention is (1) a hydraulic oil based on a fatty acid diester and / or a polyalkylene glycol, and the density of the hydraulic oil is 0.87 g / cm ³ or more at a temperature of 15 ° C. It is a hydraulic oil characterized by the fact that it can be used as a lubricating oil with minimal material changes to adjust the composition of the base oil. The effect of reducing the influence on the rubber material of the hydraulic oil containing polyalkylene glycol that can be used as a base oil, and the compressibility of the hydraulic oil by using a high-density hydraulic oil for the shock absorber The effect of improving ride comfort and handling stability by reducing and improving the response of damping force. It was difficult to achieve a balance between steering stability and steering stability, but it was possible to achieve both of them at a high level, especially in terms of high-frequency vibration, straight running stability, steering feel, and roll feeling. While exhibiting the effect that improvement can be achieved, the following aspects (2) to (13) are included.
(2) The hydraulic oil according to (1), wherein the fatty acid diester is a dibasic acid fatty acid and alcohol ester or a polyhydric alcohol and fatty acid ester.
(3) The hydraulic oil according to (1), wherein the polyalkylene glycol has an oxyalkylene group having 1 to 7 carbon atoms.
(4) The fatty acid diester is a dibasic acid fatty acid and alcohol ester or a polyhydric alcohol and fatty acid ester, and the polyalkylene glycol has an oxyalkylene group having 1 to 7 carbon atoms (1 ) Hydraulic fluid.
(5) The hydraulic fluid according to any one of the above (1) to (4), which is a hydraulic fluid for a shock absorber.
(6) The hydraulic oil according to (5), wherein the density of the hydraulic oil is in a range of 0.87 to 1.00 g / cm ³ .
(7) The hydraulic oil according to (5), wherein the base oil of the hydraulic oil is contained in an amount of 80 to 99.5% by weight.
(8) The hydraulic oil according to (5), wherein the base oil of the hydraulic oil is composed of a polyalkylene glycol and a chemically synthesized oil, and a ratio of the polyalkylene glycol in the base oil is 17% by weight or more.
(9) The hydraulic fluid according to the above (5), which is a hydraulic fluid having a friction coefficient in a range of 0.012 or less as measured under a condition of 0.06 m / s.
(10) One or more base oils selected from the polyalkylene glycol, fatty acid diesters, polyalphaolefins, and lubricating oils classified as GIII in the American Petroleum Institute (API), which are hydraulic oils in contact with the rubber material The hydraulic fluid as described in (1) above, wherein
(11) The above fatty acid diester in the base oil, the polyalphaolefin, and 5 to 60% by weight of one or more selected from lubricating oils classified as GIII in the American Petroleum Institute (API) The hydraulic oil as described in 10).
(12) The hydraulic oil according to (10), wherein the rubber material is any one of nitrile rubber, hydrogenated nitrile rubber, and fluororubber.
(13) A shock absorber using the hydraulic oil according to any one of (10) to (12) and the rubber material.

The hydraulic oil for shock absorber in the present invention has a composition that reduces the influence on the rubber material, and is useful for improving the durability of the member or preventing oil leakage. Further, by increasing the density of this hydraulic oil, the handling stability and ride comfort are remarkably improved. By simultaneously satisfying the low coefficient of friction and high density of the hydraulic fluid, these properties will be further improved. The hydraulic fluid for a shock absorber of the present invention is particularly suitable for a passenger car in which riding comfort is important, and can make the use of the passenger car comfortable for the driver and passengers. The shock absorber hydraulic oil may be applied not only to passenger cars but also to railway damper hydraulic oil.
The hydraulic oil of the present invention can be used for both a double-cylinder shock absorber and a single-cylinder shock absorber, and can be used for either a four-wheel or a two-wheel shock absorber. Is preferably used.

Further, the shock absorber hydraulic oil according to the present invention has a high density, so that the handling stability and the ride comfort are remarkably improved. A hydraulic oil that satisfies both the low coefficient of friction and the high density simultaneously will improve these characteristics. The hydraulic fluid for a shock absorber of the present invention is particularly suitable for a passenger car in which riding comfort is important, and can make the use of the passenger car comfortable for the driver and passengers.
The hydraulic oil of the present invention can be used for both a double-cylinder shock absorber and a single-cylinder shock absorber, and can be used for either a four-wheel or a two-wheel shock absorber. Is preferably used.

Claims

A hydraulic oil based on a fatty acid diester and / or a polyalkylene glycol, wherein the hydraulic oil has a density of 0.87 g / cm 3 or more at a temperature of 15 ° C.
The hydraulic oil according to claim 1, wherein the fatty acid diester is a dibasic acid fatty acid and alcohol ester or a polyhydric alcohol and fatty acid ester.
The hydraulic oil according to claim 1, wherein the polyalkylene glycol has an oxyalkylene group having 1 to 7 carbon atoms.
The fatty acid diester is a dibasic acid fatty acid and alcohol ester or a polyhydric alcohol and fatty acid ester, and the polyalkylene glycol has an oxyalkylene group having 1 to 7 carbon atoms. hydraulic oil.
The hydraulic oil according to any one of claims 1 to 4, which is a hydraulic oil for a shock absorber.
The hydraulic oil according to claim 5, wherein the density of the hydraulic oil is in a range of 0.87 to 1.00 g / cm 3 .
The hydraulic oil according to claim 5, wherein the base oil of the hydraulic oil is contained in an amount of 80 to 99.5% by weight.
The hydraulic oil according to claim 5, wherein the base oil of the hydraulic oil is composed of a polyalkylene glycol and a chemically synthesized oil, and a ratio of the polyalkylene glycol in the base oil is 17% by weight or more.
The hydraulic oil according to claim 5, which is a hydraulic oil having a friction coefficient in a range of 0.012 or less as measured under a condition of 0.06 m / s.
A hydraulic oil in contact with a rubber material, which contains the polyalkylene glycol, a fatty acid diester, a polyalphaolefin, and one or more base oils selected from lubricants classified as GIII in the American Petroleum Institute (API). The hydraulic oil according to claim 1.
The fatty acid diester in the base oil, the polyalphaolefin, and at least one selected from lubricating oils classified as GIII in the American Petroleum Institute (API) are contained in an amount of 5 to 60% by weight. Hydraulic oil.
The hydraulic oil according to claim 10, wherein the rubber material is any one of nitrile rubber, hydrogenated nitrile rubber, and fluorine rubber.
A shock absorber using the hydraulic oil according to any one of claims 9 to 12 and the rubber material.